1. Field of the Invention
The present invention relates to a novel polyolefin type resin laminate. More particularly, the present invention relates to an excellent polyolefin type resin laminate that is suitable as a stretch film for packaging food, causes no public hazards, is nontoxic, and would neither deteriorate the packaged state nor lower the commercial value of an article when the article packaged in the laminate.
2 Description of the Related Art
Recently, stretch-wrap packages are used widely because, for example, stretch-wrap packages have such features that (a) the stretch film can fit the profile of an article to be packaged without forming crumples, so that the commercial value of the appearance of the article to be packaged is increased, (b) the stretch film has a moderate gas permeability so that it can prevent the freshness of an article to be packaged such as perishable foods from lowering, and (c) efficient packaging operation can be done by using an automatic packaging machine.
The following, for example, are required for stretch films to be used in such stretch-wrap packages: a stretch film (1) should be excellent in deformation recovery property, i.e., should be high in strain recovery rate, (2) should be excellent in transparency, (3) should be excellent in fog resistance, (4) should be high in breaking extension, (5) should have a moderate gas permeability and should be low in water vapor permeability, (6) should not allow the components in the film to transfer to the food in the package, (7) should not bring about problems when it is treated as waste, and (8) can withstand cold storage and cold transportation.
Conventionally, as such stretch film, use has been made of a non-stretched film usually consisting of a soft vinyl chloride resin.
However, in the case of such soft vinyl chloride resin films, although, of the above requirements, items under (1), (2) and (4) are relatively satisfied, soft vinyl chloride resin films have, for example, such defects that (a) since the soft vinyl chloride resin film contains a large amount of a plasticizer, it is liable to cause blooming, and it is liable to transfer to the article that is packaged in the film, which is not preferable in view of food hygiene (the requirements under (3) and (6) mentioned above are not satisfied), (b) when the film is fused or burnt, it re)eases hydrogen chloride gas, which is not preferable in view of environmental hygiene (the requirement under (7) mentioned above is not satisfied), (c) when an article packaged therein is refrigerated and stored or transported, the film becomes brittle and liable to be broken (the requirement under (8) mentioned above is not satisfied), and (d) the water vapor permeability of the film is high, and the film is not suitable for packaging some types of perishable foods (the requirement under (5) mentioned above is not satisfied).
To obviate the defects of such a stretch film made of a soft vinyl chloride resin, a film made of a polyolefin type resin is suggested.
However, this film is inferior in deformation recovery property. That is, for example, when the film is pressed by one's finger, necking occurs, and the film is deformed and is hardly restored to the original shape. In the case wherein an article packaged in a film made of a polyolefin type resin is displayed on a shop front to allow consumers to watch it by freely handling it, if the article is handled many times by consumers to watch it, the state of the package becomes worsened, leading to lowering of the value of the article packaged in said film. Therefore, because the film of a polyolefin type resin has such a defect that it cannot be used in a field in packaging food wherein it is required that the packaged state would not be worsened if the package is handled many times, the field wherein the film of a polyolefin type resin is used is inevitably restricted.
On the other hand, as polyolefin type resins, butene-1 type polymers such as a butene-1 homopolymer and a copolymer of butene-1 with other .alpha.-olefin are known, and these butene-1 type polymers are used mainly to improve the heat-sealing properties of polypropylenes (Japanese Patent Application Laid-Open No. 110550/1986), but it is the present state that the application of them wherein their characteristics can be utilized to the maximum has not yet been developed fully.